1. Field of the Invention
The present invention relates to a method for driving a recording head configured to discharge an ink droplet with an electrothermal transducer that can generate thermal energy, and also relates to a recording apparatus including the recording head.
2. Description of the Related Art
An inkjet recording apparatus is a non-impact recording apparatus that performs recording on a paper or another type of sheet with ink discharged from a recording head. The inkjet recording apparatus is capable of performing high-speed recording or using various recording media and is advantageous in noise reduction. Therefore, inkjet recording apparatuses are widely used for printers, wordprocessors, facsimiles, and copying machines.
As discussed in Japanese Patent Application Laid-Open No. 2005-161614, a conventional inkjet recording apparatus has the following structure.
FIG. 13 illustrates a perspective view of an inkjet recording apparatus M1000. FIG. 14 illustrates a perspective view of the interior of the inkjet recording apparatus M1000. The inkjet recording apparatus M1000 includes a feeding unit M3022 that feeds a recording sheet and a recording unit M3000 that performs a recording operation by discharging ink onto a supplied recording sheet. As illustrated in FIG. 13, the main body of the inkjet recording apparatus M1000 is covered with a casing M1005. The feeding unit M3022 includes feeding rollers (not illustrated) that feed a recording sheet to the recording unit M3000 according to a predetermined driving signal.
The recording unit M3000 includes a guide shaft M3020 fixed to a chassis M3019 (i.e., a base frame of the inkjet recording apparatus M1000) and a carriage M4001 supporting a recording head H1001 (refer to FIG. 15). The carriage M4001 can move forward and backward in parallel with the guide shaft M3020 (i.e., X direction in FIG. 14). Then, while the carriage M4001 performs a scanning operation relative to a recording sheet, the recording head H1001 discharges ink droplets from discharge ports (not illustrated) to perform recording.
FIG. 15 illustrates a perspective view of the recording head H1001 to be mounted on the carriage M4001 of the inkjet recording apparatus M1000, with discharge ports provided at a bottom side thereof. The recording head H1001 illustrated in FIG. 15 is configured to drive an electrothermal transducer (electrothermal conversion element, energy generation element) in accordance with an electric signal to cause film boiling in ink and thereby discharge an ink droplet.
The recording head H1001 includes a holder H1500 made of a resin material and a recording element substrate H1100 attached to a lower surface of the holder H1500 and having discharge ports (not illustrated) from which ink droplets can be discharged. The recording head H1001 includes an electric wiring board H1300 that supplies electric signals to the recording element substrate H1100. The holder H1500 has a configuration capable of holding a plurality of ink tanks (not illustrated) and is detachably engaged with the above-described carriage M4001 (refer to FIG. 14).
FIG. 16 is an exploded perspective view of the recording head H1001 illustrated in FIG. 15. A discharge port surface H1550, configured into a flat surface, is provided on the bottom of the holder H1500, as illustrated in FIG. 16. A supporting recess 1501, capable of accommodating the recording element substrate H1100, is formed on the discharge port surface H1550. A plurality of ink channels H1502, each supplying an ink from an ink tank (not illustrated) to the recording element substrate H1100, is opened to the supporting recess 1501.
The recording element substrate H1100 is made of a silicon-made substrate and is rectangular in external shape. A plurality of discharge port groups H1101, each group including a plurality of discharge ports, is provided on the recording element substrate H1100. The discharge port groups H1101 are arrayed at equal intervals in the scanning direction of the carriage M4001 (X direction in FIG. 15). Each discharge port group H1101 includes a plurality of discharge ports arrayed in a direction perpendicular to the scanning direction of the carriage M4001 (Y direction in FIG. 15) in a state where the recording head H1001 is assembled with the carriage M4001.
The electric wiring board H1300 is, for example, made of a tape automated bonding (TAB) film which is bendable. The electric wiring board H1300 has one end adhering to the bottom of the holder H1500 and the other end fixed to a side surface of the holder H1500. The electric wiring board H1300 includes an aperture H1301 that faces the bottom of the holder H1500 and a contact portion H1350 that contacts an external electric connector portion (not illustrated) at the other end. For example, the TAB film has a thickness of 0.12 mm.
Next, an example structure of the recording element substrate H1100 placed in the supporting recess H1501 is described in more detail below.
FIGS. 17A and 17B illustrate an example structure of discharge ports and a peripheral structure of the recording head H1001 illustrated in FIG. 15. FIG. 17A illustrates the bottom of the recording head H1001 that includes discharge ports, and FIG. 17B illustrates a cross-sectional view of the recording element substrate H1100 taken along a line 17B-17B of FIG. 17A.
FIG. 18 illustrates an enlarged cross-sectional view of the recording element substrate H1100. The recording element substrate H1100 has a laminated structure including an orifice plate H1115a including a plurality of discharge ports H1101a and a heater board H1115b including ink supply ports H1101b, as illustrated in FIG. 18. The orifice plate H1115a, which is made of a thin plate member, includes a total of six discharge port groups H1101 arrayed in a predetermined direction. Each discharge port group H1101 includes a plurality of discharge ports H1101a as illustrated in FIG. 17A. The number of the discharge port groups H1101 corresponds to the number of ink tanks (not illustrated) installable on the holder H1500 (refer to FIG. 16). Each discharge port group H1101 can discharge an ink supplied from a corresponding ink tank (not illustrated).
The ink supply port H1101b of the heater board H1115b, although not illustrated, can be formed as an elongated hole extending in parallel with the discharge port group H1101 illustrated in FIG. 17A. One ink supply port H1101b is formed for each discharge port group H1101 on the orifice plate H1115a, so that ink can be supplied to respective discharge ports H1101a of each discharge port group H1101.
Although not illustrated, a plurality of heat generating resistors (electrothermal conversion elements) is provided on a surface of the heater board H1115b to which the orifice plate H1115a adheres. The heat generating resistors, each serving as “energy generation element”, are disposed at equal intervals at both sides of the ink supply port H1101b. Furthermore, electric wiring (not illustrated) is provided on the same surface of the heater board H1115b. The electric wiring supplies electric power to the above-described heat generating resistors. The wiring is connected to electrode pads (not illustrated) provided at both sides of the heater board H1115b in the longitudinal direction.
As illustrated in FIG. 17A, the supporting recess H1501 in which the recording element substrate H1100 can be disposed has a rectangular outer shape larger than that of the recording element substrate H1100. The supporting recess H1501 has a predetermined depth so that the recording element substrate H1100 and the electric wiring board H1300 are positioned on the same plane when the recording element substrate H1100 is placed in the supporting recess H1501 as illustrated in FIG. 17B. This plane can be referred to as “discharge port surface.”
The recording element substrate H1100 is disposed and bonded approximately at the center of the supporting recess H1501, so that the ink supply port H1101b can communicate with the ink channel H1502 of the holder H1500.
When the recording element substrate H1100 is disposed in the supporting recess H1501, a groove H1503 (refer to FIG. 17B) is formed around the recording element substrate H1100. More specifically, the groove H1503 is positioned between an outer peripheral surface of the recording element substrate H1100 and an inner peripheral surface of the supporting recess H1501. The groove H1503 is sealed with first sealing members M1303a and second sealing members M1303b. The first sealing members M1303a are disposed along short sides of the recording element substrate H1100, and the second sealing members M1303b are disposed along long sides of the recording element substrate H1100.
A lead H1302 on the electric wiring board H1300 provides an electric connection between the recording element substrate H1100 and the electric wiring board H1300. The lead H1302 extends along each long side of the rectangular aperture H1301 formed on the electric wiring board H1300. Accordingly, the lead H1302 and the electrode pad (not illustrated) of the recording element substrate H1100 are electrically connected along the long side of the recording element substrate H1100. This electric connection can be realized by forming a bump on the electrode pad (not illustrated) of the heater board H1115b and mounting the lead H1302 using the TAB mounting method. The electric connecting portion (not illustrated) can be sealed with a sealing member.
According to the above-described recording head H1001, a heat generating resistor (not illustrated) of the recording element substrate H1100 is driven in response to an electric signal input via the contact portion H1350 of the electric wiring board H1300. Then, the recording head H1001 performs recording by discharging ink from the discharge port H1101a. 
The minimum input energy required for generating bubbles in the ink (i.e., bubbling threshold energy) is not constant for each recording head because of differences in manufacturing processes of the heater board H1115b (which may have different dimensions in the electrothermal conversion member and the electric wiring).
Accordingly, if the energy applied from the inkjet recording apparatus is constant, following problems arise. For example, if the applied energy is excessively lower than the bubbling threshold energy, the ink does not bubble. On the other hand, if the applied energy is excessively higher than the bubbling threshold energy, an excessive load is applied to the electrothermal conversion member and the recording head may be damaged.
Hence, manufacturing processes of a conventional recording head include measuring the bubbling threshold energy for each recording head and classifying the recording head into one of a plurality of ranks according to the measured bubbling threshold energy. On the other hand, an inkjet recording apparatus identifies the rank of an associated recording head and adjusts a driving voltage or a driving pulse width for the recording head according to the rank.
Furthermore, to enable an inkjet recording apparatus to discriminate the rank of a recording head, a dedicated wiring is provided on a relay wiring substrate and a predetermined portion of the wiring is cut according to the rank so that the state of electric connection between the inkjet recording apparatus and the recording head can be changed.
Furthermore, a memory or a comparable storage element can be provided on a recording head. The storage element stores data relating to the rank of each recording head. The inkjet recording apparatus reads the data stored in the storage element of the recording head.
Similarly, an inkjet recording apparatus can identify characteristics that require changing of driving conditions, in addition to the bubbling threshold energy.
The above-described method enables an inkjet recording apparatus to identify driving conditions of a recording head. However, the following problems arise if the above-described method is employed.
First, a new process is required to inspect a printed material when each recording head is delivered from a factory and measure a minimum energy value to be input into a recording head. Furthermore, another process is required to store the information relating to a measured energy value into the storage element of the recording head. Accordingly, the throughput in the delivery process for a recording head (manufacturing process) deteriorates.
Furthermore, according to the recording head discrimination method that includes cutting a dedicated wiring according to a measured energy value, a special tool is required to cut the wiring. The work in the delivery process becomes troublesome due to cutting of the wiring.